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Product Manager’s Corner

In a previous post, we showed an example of how a topography could be modeled in 3DEC using the ‘octree’ approach. First, a geometry surface is imported (e.g., a dxf file) and a small number of blocks are created. Then, each block that is touching the geometry surface is split into eight smaller blocks. This continues until there is a satisfactory representation of the surface geometry (see...

3DEC is commonly used to model rock masses close to the earth’s surface. In these situations, the in-situ vertical stress at each point can be calculated from the weight of overlying material. The horizontal stresses often are assumed to be some proportion of the vertical.

3DEC provides a command, insitu topo, to calculate these initial stresses for each zone. However, this calculation used to be so slow that is was not of practical use. With the latest...

3DEC Version 5 can build and use Discrete Fracture Networks (DFNs) to create joints in 3DEC models. But, because all blocks in 3DEC must be convex, cuts must split blocks entirely, even if the fracture only passes partway through the block. This problem is resolved by assigning properties to the subcontacts lying within the fracture that differ from those lying outside of the fracture — which is easily accomplished with the change dfn command.

As promised last time, this post talks about contouring of zone quantities such as stress and strain. As you probably know, some data is associated with gridpoints (e.g. displacements and velocities) and some data is associated with zones (e.g. stresses and strains). Methods for contouring data at discrete points are well known; therefore the contouring of gridpoint data is included in 3DEC. These contours can be accessed through Blocks – Contours in the...

Most of the problems that occur when running 3DEC models are the result of bad block geometries. 3DEC offers the ability to cut up blocks to any angle at any size. This is a very powerful feature, but unfortunately this power also allows for the creation of very thin or very small blocks. These can cause problems when deformation occurs and blocks start to collapse, resulting in error messages such as ‘negative volume zone’ or ‘bad face normal’.

Plotting excavated volumes in 3DEC is easy – simply check the box to show excavated volumes. But what if you want to see the stresses and displacements on the surface that has not been excavated? Until recently, this has not been easy.

In 3DEC 5.2, a recently added new feature enables plotting only faces with a given surface region. To use it, assign a surface region to the faces on the surface of a tunnel and then, when plotting blocks, check the box to plot only...

Users of UDEC will be familiar with Voronoi jointing capabilities that allow you to create polygonal blocks. This allows you to simulate a background fracturing that could represent mineral grain boundaries or some dense jointing in a rock mass. There is no such capability (yet) in 3DEC. However, you can easily create a model composed of tetrahedral blocks. Here’s how.

In 3DEC, it is easy to see if joints have failed by plotting Joints – Slip. This will plot small cubes at each subcontact colored by their state (slipping, slipped in past, or failed in tension). However, it is not so easy to find the joints that are close to failure but have not yet failed. You could run a factor of safety analysis to find the critical joints, but this can be very slow for large 3D models. Another alternative is to plot the strength-stress ratio...

3DEC includes the ability to simulate fluid flow through joints. The calculations are fully coupled such that pressure changes can cause displacements of the solid. However, often we don’t want to deal with the complexity of modelling fluid flow through joints, or even modelling fluid flow at all.

3DEC also therefore provides a much simpler approach to considering pore pressures. A water table can be specified (as a simple plane, or an imported surface geometry) and pore pressures...

Welcome to the 3DEC Product Manager’s Corner. This is a new forum where the product manager (me) will discuss interesting topics relating to 3DEC, including tips and tricks, answers to frequently asked questions and new research and development initiatives. This is meant to be an informal meeting place for 3DEC users, so comments and suggestions are certainly welcome.

To kick things off, here is a sneak peak and the next version. Note the drop down menu for the quantity being...